1. Field of the Invention
This invention relates to a color sensor capable of performing data processing for distinguishing a color at high speed under a light source having a flicker such as a fluorescent lamp.
2. Prior Art Statement
A conventional color sensor utilizing a tristimulus value direct reading method which has been generally used, must have an exclusive standard light source. In this color sensor, the color distinction is made in the state that extraneous light is blocked to some extent or an object is illuminated by a standard light source brighter than the extraneous light, such as a light source, for example, of 2,000 lux against an extraneous light of 500 lux.
However, since the conventional color sensor requires an exclusive standard light source as described above, it is very difficult for the conventional color sensor to be used on an actual production line. Therefore, a color sensor which can be used under a fluorescent lamp ordinarily used as factory illumination, is strongly demanded.
The present inventor has proposed a color distinction device capable of solving the above-mentioned problem and improving the capability of distinguishing red-purple colors (Japanese Patent Public Disclosure No. SHO 61(1986)-262623, U.S. patent application Ser. No. 4,766,702. The proposed color distinction device comprises optical sensing devices sensitive to three primary colors of red, green and blue respectively, and a complementary sensor. In this device, the capability of distinguishing colors is improved by using an output from the complementary sensor.
However, when the color sensing is performed at high speed under a fluorescent lamp used as industrial illumination, the flicker of light due to the frequency of an electric power source of a fluorescent lamp offers a large interference. In the above-mentioned color distinction device, an electric filter circuit is used in order to remove an influence of flicker due to the frequency of an electric power source of a fluorescent lamp. Although a correct color distinction can be made if the filter circuit is employed, the circuit takes a comparatively long time for processing, i.e., usually 2 or 3 seconds. Therefore, sometimes the color sensing is unable to cope with the high speed of the production line. That is, since the relative composition ratio of the three primary colors is changed by the timing for processing the three primary colors it fails to make a correct color distinction, and the filter is connected to a rear part of a current to voltage converter (an I/V converter) to obtain a direct current signal in order to remove undesired influence due to the flicker. However, since the processing time for the filter according to this method requires 2 to 3 seconds, high speed distinction is difficult to obtain.
Therefore, if a method for eliminating the flicker at high speed can be established, a correct color distinction can be made in the above-proposed device even if the speed of the production line is comparatively high.